Slow Magnetic Relaxation in One-Dimensional Azido-Bridged CoII Complexes

• Published in: Inorganic chemistry Vol. 56; no. 14; pp. 8058 - 8067
• Main Authors: Zhao, Xin-Hua, Deng, Lin-Dan, Zhou, Yan, Shao, Dong, Wu, Dong-Qing, Wei, Xiao-Qin, Wang, Xin-Yi
• Format: Journal Article
• Language: English
• Published: American Chemical Society 17.07.2017
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/acs.inorgchem.7b00736

Crystal structures and magnetic properties of three one-dimensional (1D) azido-bridged cobalt­(II) chains with different amide ligands (L), [Co2(N3)4(DMF)3] (1), [Co4(N3)8(DEF)5] (2), and [Co2(N3)4(DIPF)2] (3) (DMF = N,N-dimethylformamide, DEF = N,N-diethylformamide, and DIPF = N,N-diisopropylformamide), are reported to investigate the influence of L on their structures and magnetic properties. Single-crystal X-ray crystallographic analysis revealed that, although 1–3 all consist of cobalt chains bridged by end-on (EO) azides, the coordination geometry of the CoII ions and the repeating units of the 1D structures are quite different. As the size of L increases, the ratio of L to CoII decreases from 6:4 in 1 to 5:4 and 4:4 in 2 and 3, respectively. In 1, two [CoN5O1] and two [CoN4O2] distorted octahedra form the {[CoN5O1]­[CoN4O2]2[CoN5O1]} tetramers (denoted as Co4A), which are linked to each other by sharing the N–N edge to form the chain. Similarly, the chain structure of 3 is constructed from a similar tetramer unit {[CoN5]­[CoN4O2]2[CoN5]} (denoted as Co4B), where half of the CoII centers are in the [CoN5] trigonal bipyramid because of the larger steric effect of the DIPF ligand, while, for compound 2 of the medium-sized amide, it has the transition structure between those of 1 and 3. The chain is composed of two different repeating units: Co4A unit similar to that in 1 and Co4B unit similar to that in 3. Because of their similar structures, compounds 1–3 exhibit analogical magnetic properties. Direct-current magnetic measurements demonstrated that all compounds show intrachain ferromagnetic coupling through the EO azides and interchain anti-ferromagnetic interactions. Alternating-current data revealed the slow magnetic relaxation in the anti-ferromagnetic ordered phases. While compound 1 exhibits spin glass behavior, compounds 2 and 3 behave as the single-chain magnets. This difference might come from the interference of the anti-ferromagnetic ordering on the magnetic dynamic of the magnetic chain.